2-Difluoromethoxy-1,1,1,2-tetrafluoroethane (CHF.sub.2 OCHFCF.sub.3) is an important inhalation anesthetic particularly suited for administration to patients during outpatient surgery due to its rapid rate of recovery.
A common method of preparing CHF.sub.2 OCHFCF.sub.3 is by reacting isoflurane (CHF.sub.2 OCHClCF.sub.3) with a fluorinating agent such as BrF.sub.3. Isoflurane, however, is expensive and significantly increases the cost of producing CHF.sub.2 OCHFCF.sub.3. Isoflurane's expense is mainly due to its method of preparation from trifluoroethanol (CF.sub.3 CH.sub.2 OH) and chlorodifluoromethane (CF.sub.2 HCl). Trifluoroethanol is both difficult to produce and expensive to obtain.
In view of the above, the compound fluoral methyl hemiacetal (CF.sub.3 CH(OH)OCH.sub.3) is an attractive alternative starting material for the preparation of CHF.sub.2 OCHFCF.sub.3. Fluoral methyl hemiacetal can be economically produced in high yield from the reaction of fluoral (CF.sub.3 CHO) with methanol, both of which are inexpensive materials.
Fluoral methyl hemiacetal has indeed been used as a starting material for the production of CHF.sub.2 OCHFCF.sub.3. For example, U.S. Pat. No. 3,980,714 discloses reacting the hemiacetal with PCl.sub.5 or SOCl.sub.2 to thereby replace the hydroxy group with a chlorine atom. In a process disclosed in U.S. Pat. No. 3,981,927, the hemiacetal is reacted with a compound of the formula R'R'NCF.sub.2 CHFCl to replace the hydroxy group with a fluorine atom. The above procedures are disadvantageous because they employ complex and costly reagents to produce the desired product.
The product of the first reaction, CF.sub.3 CHClOCH.sub.3, is photochemically chlorinated to produce the compound CF.sub.3 CHClOCHCl.sub.2, which is then reacted with a fluorinating agent to produce the desired product CHF.sub.2 OCHFCF.sub.3, as disclosed in German Offen. 2,823,969. The fluorinated product of the second reaction (CF.sub.3 CHFOCH.sub.3) is reacted with chlorine to produce a compound of the formula CF.sub.3 CHFOCHCl.sub.2 which, in turn, is reacted with a fluorinating agent, such as hydrogen fluoride, to produce the desired product CHF.sub.2 OCHFCF.sub.3 This latter reaction is disclosed in U.S. Pat. No. 3,535,388.
These problems are resolved in accordance with the present invention which provides an improved, less costly method for the preparation of CHF.sub.2 OCHFCF.sub.3 from inexpensive starting materials via the hemiacetal.